1. Technical Field of the Invention
The present invention relates to control of the repetition frequency of a laser light pulse.
2. Related Art
A system which maintains a difference between the repetition frequencies of two lasers to be constant by independently controlling the repetition frequencies of the two lasers has conventionally been known (refer to FIG. 18 and [0077] of a patent document 1 (Japanese Patent No. 4565198), for example).